Actuating drives having a spring return feature are often used to operate final control elements, more particularly valves, in heating, air-conditioning and ventilation systems. Drives of this kind, hereinafter called spring return drives, have a return spring which is tensioned by a motor having a reduction gearing. The energy stored in the return spring Is released when the electric motor becomes currentless. The spring return feature ensures that in the event of a power failure the final control element moves into a safety position, normally the closed position.
Actuating drives are in practice fitted to both the left side and right side of final control elements, for example, ventilation valves. The choice of side for assembly depends upon the space available in an existing system. However, the direction of rotation of a valve alters with a change of the assembly side For example, if a valve opens from the left as considered clockwise, it opens from the right as considered anticlockwise.
Spring return actuating drives generally have only a single return spring. The spring return movement and the direction of rotation of the actuating drive output shaft associated with the final control element are fixed. In the prior art a specific direction of assembly is always associated with the actuating drive.
It is known to turn the output shaft for connection to the final control element through 180.degree. for adaptation to the direction of valve rotation. However, this leads to the disadvantage in virtually all cases that, after the output shaft has been turned, control and connection members, for example, auxiliary switches, hand tensioning, connection terminals, circuit boards or the like are accessible only with difficulty, if at all.
A problem which the invention intends to solve is to provide a transmission for a spring return actuating drive which enables the output shaft associated with the final control element to reverse its direction of rotation.
The subject of the invention and the solution of the problem is a transmission for an actuating drive having a spring return feature, the transmission having:
a drive pinion associated with the actuating drive; PA1 an intermediate pinion meshing with the drive pinion; PA1 an output shaft having a clutch for a final control element, and PA1 two gears which are disposed axially and consecutively on the same spindle, each gear having external toothing and a rotatably mounted hub so extending around the output shaft as to leave an annular gap between the same and the hub, PA1 wherein the drive pinion meshes with the external toothing of one of the two gears and the intermediate pinion meshes with the external toothing of the other gear and a coupling sleeve is disposed in the annular gap between the output shaft and the gears, is releasably connected to the output shaft and is coupled positively with the hub of one of the gears.
The intermediate pinion driven by the drive pinion rotates in the opposite direction thereto consequently, the transmission according to the invention has two gears which rotate synchronously in time with the drive pinion but in different directions. The coupling sleeve is interchangeable and represents, as it were, a switching element which selectively transmits the movement of one or other gear to the output shaft associated with the final control element. The coupling sleeve does not need its own mounting on the housing side and is therefore readily interchangeable.
Various constructional solutions present themselves for the further development of the transmission according to the invention. In a preferred construction of the transmission according to the invention, the hubs of the gears each have internal toothing engageable with a toothed ring on the periphery of the coupling sleeve. This construction ensures a uniform transmission of the torque. In a further development of the invention, the coupling sleeve has a plain cylindrical part into which the toothed ring merges and which is rotatable relatively to the hub of the gears. Conveniently, the hubs of the two gears driven by the drive pinion or intermediate pinion are identical, i.e., they have the same dimensions and the same toothing. The coupling sleeve extends through the annular gap defined by the two hubs, one half of the coupling sleeve having a toothed ring corresponding to the internal toothing of the hubs while the other half is plain cylindrical. The coupling sleeve is introducible at choice into the annular gap between the hubs and the output shaft on either the end face facing the actuating drive or on the end face remote therefrom. In a preferred embodiment, a catch spring secured to the output shaft is provided to secure the coupling sleeve.
The actuation distance of the spring return drive is usually so limited that the output shaft makes angular movements of at most 180.degree., the rotation being either clockwise or anticlockwise depending upon how the coupling sleeve is fitted. The gears consist of the hub and a circle segment disc on whose periphery the external toothing is disposed. The alignment of the circle segment disc and the length of the arc segment are adapted to the actuation travel of the spring return drive and to the direction of output shaft rotation.
The invention will be described hereinafter with reference to a drawing which illustrates just one embodiment and in which in diagrammatic form: